1) Field of the Invention
The present invention relates to a novel polycarbonate resin with excellent heat resistance, good balance of mechanical properties and low birefringence.
2) Prior Art
At present, a polycarbonate resin made from 2,2-bis(4-hydroxyphenyl)propane (so-called bisphenol A) has been used in a wide field because it has high transparency, good balance of mechanical properties and high heat resistance. In detail, it has been applied to various materials including optical materials such as optical discs, prisms, optical lenses and optical films and transparent structural materials such as cups as a substitute of glass, transparent boards for putting into a window frame and transparent roof plates of arcade.
However, a polycarbonate resin made from bisphenol A has a defect that it cannot be applied in the field to require a stiffness of flexural elastic modulus more than 2300 MPa because it has a flexural elastic modulus of 2300 MPa. In order to increase its stiffness, it has been widely conducted to mix an inorganic filler(s) such as glass fiber, carbon fiber and boron nitride in it. However, there was a problem that such organic fillers cannot be applied in the field to require transparency since kneading of such inorganic fillers cause remarkable deterioration of transparency. For example, although there is a case that a glass with a refractive index difference of 0.01 or below is mixed in a polycarbonate resin, haze is large and transparency is quite insufficient (Japanese Patent Kokai (Laid-open) No. 6-184424). Further, although there is a case that a glass with a refractive index of 1.570 to 1.600 and a plasticizer are mixed in a polycarbonate resin, haze is large and transparency is quite insufficient (Japanese Patent Kokai (Laid-open) No. 2002-020610).